Reducing crown flash in injection-molding processes

Abstract

Crown-flash-reduction systems, methods, and apparatuses for actively reducing the likelihood of formation of crown flash on injection-molded objects. The active reduction includes moving at least one of a valve member and a mold gate periphery in a manner that actively weakens or separates molding material present in a molded object from molding material present in the closed mold gate prior to or in conjunction with de-molding the molded object.

What is claimed is: 
     
         1 . An injection-molding system, comprising:
 a mold that includes a mold cavity and a gate in fluid communication with said mold cavity, said mold designed and configured for molding a molding and said gate having a periphery;   a runner operatively configured for injecting a molding material into said mold cavity via said gate, said runner including a valve member operable to close said gate to flow of the molding material by movement of said valve member into said gate; and   a crown-flash-reduction system designed and configured to actively participate in separating molding material present in the molding from molding material present between said valve member and said periphery of said gate when said valve member is positioned in said gate.   
     
     
         2 . An injection-molding system according to  claim 1 , wherein said runner includes a first actuator designed and configured to actuate said valve member in a first set of motions so as to open and close said gate, said crown-flash-reduction system including a second actuator designed and configured to actuate said valve member in a second set of motions different from said first set of motions. 
     
     
         3 . An injection-molding system according to  claim 2 , wherein said valve member comprises a valve stem having a longitudinal axis and said first actuator is designed and configured to reciprocate said valve stem along said longitudinal axis, said second actuator being designed and configured to move said valve stem in a direction substantially perpendicular to said longitudinal axis. 
     
     
         4 . An injection-molding system according to  claim 3 , wherein said second actuator is designed and configured to rotate said valve stem about said longitudinal axis. 
     
     
         5 . An injection-molding system according to  claim 4 , wherein said valve stem has a tip region that extends into said gate when said gate is closed, said tip region including at least one interlock feature designed and configured to create a mechanical interlock between said tip region and the molding material present between said tip region and said periphery of said gate when said tip region is positioned in said gate. 
     
     
         6 . An injection-molding system according to  claim 5 , wherein said tip region has a lateral surface relative to said longitudinal axis, said at least one interlock feature including surface roughening of said lateral surface. 
     
     
         7 . An injection-molding system according to  claim 5 , wherein said tip region has a lateral surface relative to said longitudinal axis, said at least one interlock feature including a plurality of recesses formed in said lateral surface. 
     
     
         8 . An injection-molding system according to  claim 1 , wherein said crown-flash-reduction system includes a moveable member engaged with said mold and movable relative to said mold, said movable member defining said inner periphery of said gate. 
     
     
         9 . An injection-molding system according to  claim 8 , wherein said gate has a central axis parallel to flow of the molding material therethrough, and said movable member is operable so as to rotate about said central axis. 
     
     
         10 . An injection-molding system according to  claim 9 , wherein said movable member includes at least one interlock feature on said inner periphery of said gate. 
     
     
         11 . An injection-molding system according to  claim 10 , wherein said at least one interlock feature includes surface roughening on said inner periphery of said gate. 
     
     
         12 . An injection-molding system according to  claim 10 , wherein said at least one interlock feature includes a plurality of recesses formed in said inner periphery of said gate. 
     
     
         13 . An injection-molding system according to  claim 1 , further comprising a control system designed and configured to generate a crown-flash-reduction control signal for controlling said crown-flash-reduction system. 
     
     
         14 . An injection-molding system according to  claim 13 , further comprising a de-molding system, said control system designed and configured to generate a de-molding control signal for controlling said de-molding system. 
     
     
         15 . An injection-molding system according to  claim 14 , wherein said control system is designed and configured to generate said crown-flash-reduction signal prior to said de-molding signal. 
     
     
         16 . An injection-molding apparatus configured for injecting a molding material into a mold cavity via a mold gate having a periphery, the injection-molding apparatus comprising:
 a valve assembly comprising a valve member that is designed and configured to, during molding operations:
 reciprocate in a first motion between 1) an open position in which the gate is open to flow of the molding material and 2) a closed position in which said valve member extends into the gate so as to effectively close the mold gate to the flow of the molding material; and 
 while said valve member is in said closed position, move in a second motion that is different from said first motion and is selected to participate in separating molding material in the mold cavity from molding material present between said valve member and the periphery of the mold gate. 
   
     
     
         17 . An injection-molding apparatus according to  claim 16 , wherein said valve member has a longitudinal axis and said first motion is along said longitudinal axis and said second motion is in a plane substantially perpendicular to said longitudinal axis. 
     
     
         18 . An injection-molding apparatus according to  claim 17 , wherein said second motion is rotational motion about said longitudinal axis. 
     
     
         19 . An injection-molding apparatus according to  claim 17 , wherein said valve assembly further comprises a first actuation system designed and configured to move said valve member in a reciprocating motion along said longitudinal axis, and a second actuation system designed and configured to move said valve member in a rotational motion about said longitudinal axis. 
     
     
         20 . An injection-molding apparatus according to  claim 16 , wherein said valve member has a tip portion that extends into the mold gate when the mold gate is closed, said tip portion having a lateral surface that includes at least one interlock feature designed and configured to provide a mechanical interlock between said tip portion and the molding material present between said tip portion and the inner periphery of the mold gate. 
     
     
         21 . An injection-molding apparatus according to  claim 20 , wherein said at least one interlock feature comprises a plurality of recesses. 
     
     
         22 . An injection-molding apparatus according to  claim 21 , wherein said plurality of recesses comprises a plurality of grooves. 
     
     
         23 . An injection-molding apparatus according to  claim 22 , wherein said valve member has a longitudinal axis and each of said plurality of grooves has a longitudinal axis that extends along said longitudinal axis of said valve member. 
     
     
         24 . A method of injection molding a molding, comprising:
 injecting a molding material into a mold cavity via a gate so as to form the molding, wherein the gate has a periphery;   positioning a valve member in the gate in a manner that substantially closes the gate to flow of the molding material into the mold cavity; and   weakening or separating connection between molding material present in the molding from molding material present between the valve member and the periphery of the gate so as to limit formation of crown flash during de-molding of the molded part.   
     
     
         25 . A method according to  claim 24 , wherein said weakening or separating includes moving at least one of 1) the valve member and 2) a periphery of the gate. 
     
     
         26 . A method according to  claim 25 , wherein said moving includes moving only the valve member relative to the periphery of the gate. 
     
     
         27 . A method according to  claim 25 , wherein said moving includes moving only the periphery of the gate relative to the valve member. 
     
     
         28 . A method according to  claim 25 , wherein said moving includes moving the valve member and periphery of the gate in synchronicity with one another.